Process of separating impurities from metals or alloys



a 1944- B. BLUMENTHAL 2,348,719

PROCESS OF SEPARATING IMPURITIES FROM METALS 0R ALLOYS Filed Nov. 1, 1941' IN VEN TOR.

9*. a l'i'fia -4r70/e/vEY ming metals.

"Patented May 16, 1944 PROCESS OF SEPARATI NG IMPURITIES FROM METALS OB ALLOYS Bernhard Blllmen'thal; Perth'Amboy, N.

signor to American smelting and Refining C0217 gany, New York, N. Y., a corporation of New ersey Application Novembcr 1, 1941, Serial No. 417,449

This invention relates to the refining of metals and more particularly to a process of separating impurities from lead, tin and their alloys. The process is. applicable for treating, white metal," solder, type metal, teme, babbitt and similar bearing metals, as well as grid and coffln trim-- Briefly, the invention resides in the discovery that relatively small amounts of impurities in metals and alloys can be economically and etfectively removed by liquating the metal and simultaneously brushing or scraping the surface trated at I].

of the melt until tests indicate the impurities have been separated or their concentration lowered to thedesired point. In metallurgical refining processes, it has been conventional practice to employ dressing and skimming operations, for example, in softening lead bullion. The ordinary drossing and skimming operation, however, is not applicable for effecting the removaLof impurities when present in very small amounts, for instance on the' order or 0.01% or as low as 0.001%. Further, the usual drossing treatment'is inadequate to accomplish;

separation of impurities from metals where there is very little difference between the specific gravity of the metal and the impurities. -Slmilarly, the conventional drossing operation is inapt where the solubility limit of the substance to be separated is only slightly below or at theconcentration to which the impurity is to be lowered. Further, removal ofimpurities by the customary drossing and skimming operations is ineffective where the impurities are suspended as suspensoids in the melt, or where various combinations of the aforementioned conditions are present. In all these cases it is impossible, to'

remove the impurities by the ordinaryv skimming operation because there is no appreciable amount of skimmings formed which can be collected.- such operation merely stirs up the melt and dis-, perses the impurities therein.

The process or this invention, however, overcomes these difiiculties and provides a simple and highly eflicient method oi separating impurities, J whether in the form oireadily separable 'compounds or substances which are retained as suspensoids in the metal. This is theprincipal obiect of the present invention. Other objects and advantages of the invention will become-ap-' parent as the process is explained in detail.

For a more detailed description of my invention, the same is described in connection with a suitable form ofapparatus useful for carrying out thelimproved process. Such an apparatus is 8 Claims. (01. 15-93) illustrated in the accompanying drawingand comprises a kettle l5. formed of suitable material, in which the metal to be refined is placed. Suitable means is provided for supportin the kettle 15, as shown at It, and arrangement is made for heating the same as generally illus- A rotatable blade or paddle member I! is mounted on theshait 19 which is supported on the cross frame members 20 spanning the kettle. The motor reduction means 2| is drivingly connected to the shaft l9 and rotates the paddle at the desired 'R. P. M. Vertical adjustment of the paddle l8 onfthe shaft is is provided so that the paddle can be properly positioned with respect to the surface of the melt.

In operation, the metal to be refined is placed in the kettle and heated to form a meltas indicated at 22, and the paddle I8 is adjusted to dip very slightly into the metal bath. During liquation oi: the melt, the paddle is rotated. By re- "peatedly' moving the paddle over the surface of the melt, metal is continually exposed to oxidatiqn producing skimmings, which, as the paddle rotates, are brushed towards the sides of the kettle as shown at 23. As this operation continues the impurities migrate or float gradually to the surface and are wrapped up in the skimmings which are being continuously formed and scraped aside by the rotating paddle l8., Skimmings may. be formed by other conventional methods with or without the formation of oxide skimmings. All that is required is that sufllcient amount of skimmings be formed in which the substance or substances to be separated from the melt can be effectively gathered and removed.

The rotational speed of the paddle depends primarily on the surface area of the melt being treated and in each case is regulated so that the skimmings are not spattered out of the kettle,-

butmerely pushed aside to expose fresh metal without appreciably stirring or agitating the body of the melt. border to obtain the improved results, it is essential that the paddle be arranged to continually scrape aside the skimmings as Y they form while the metal is maintained unagitated and at such a temperature that the impurities or substances to be removed tend to separate out and move upwardiywhereupon they come in contact with. the skimmings and are mechanically occluded therewith. Preferably I the temperature of the metal being treated is held within-a narrow range such as will maintain the'metal in a substantially liquidstate and wherein the solubility ofthe substances to be removed'from the melt are at a minimum. The

temperature usually is as low as possible, that is, just high enough to change the metal or alloy being treated from a solid to a liquid or partially liquid state. In each instance the physical conditions imposed on the melt are such as to create a tendency for the impurities, even though slight. to segregate from the base metal and .contact the skimmings.

The following examples are given to show how effective my new process is in refining various kinds of metals and alloys. It will be understood,

2 was treated as thereindescribed. In this instance the type metal contained 0.01% zinc however, that the examples are merely typical and are notlimitative of my invention.

Example 1 One hundred and fifty pounds of Linotype metal containing principally lead, with 12% antimony, 4% tin and having a sulphur content of 0.0016% was treated by my process at between 475 F, and 525 F. for approximately forty minutes. After removing the skimmings at the end of this'time, it was found that the sulphur con-- tent was only 0.0005%.

About 24 ounces of skimmings were formed or approximately 1% of the total weight of the melt. The surface area of the melt was about .32 square inches and the di-.

ameter of the area covered by the paddle approximated '7 inches. The'paddle wasrotated at R. P. M.'

A conventional practice of removing sulphur from white metals: comprises the introduction of caustic soda or the like alkaline earth compound. The process of this invention eliminates the necessity of adding substances to-efiect the removal of small amounts of sulphur; and produces a metal which is substantially free from impurities. Further, the total weight of the skimmings produced during the process is much less than in the case of ordinary drOssing and skimming operations. This lowers the cost of the refining operation.

Example 2 Onepoundand ten ounces of Linotype metal, of

similar composition as Example 1 but containing 0.0056% sulphur, was treated in a small research laboratory apparatus, comparable to that illustrated in the accompanying drawing, for ten minutes and while heated to about 540? F. The

surface area of the melt was approximately 10 square inch and the paddle was rotated at 100 R. P. M. The area scraped, by the paddle had an approximate diameter of about 2 inches. After I removal of the skimmings, the resultant metal analyzed only 0.0002% sulphur.. One-half ounce of skimmings was formed constituting about 2% of the melt,

. Example 3 A similar weight of Linotype metal, as in Example 2. containing'0.011% aluminumwastreated att540 E. as described. In this case the aluminum was entirely removed. g

In the usual practice, the last traces of aluminum in type metals are removed by treating the metal, either with metallic alkalies or with molten alkaline salts using coombinations of.

caustic soda, sodium carbonate, or alkali chlorides. My process, however, avoids the use of addition compounds and provides a more eflective and less costly method of separating aluminum;

Example 4 A like quantity ofLinotypemetalas inExample steam. This producesa large amount oi dross and involve the loss of tin. Since zinc-considerably increases the rate of drossing of type metals, when present, his necessary to remove it completely, and my process provides a simple and improved method for doing this.

Example 5 A solder comprising approximately 60% lead and 40% tin, and containing 0.016% nickel, was treated as described in Example 2. After treatment, the nickel content was found to have been lowered to 0.008%.

In the customary kettle operations it is difllcult to remove small amounts of nickeLwhereas by employing the process of this invention'it is easy to produce metal having less than 0.01% nickel. results attained by prior methods of refining.

Example 6 Linotype metal containing 0.06% tellurium was treated by my process, as'described in Example 2, at a temperature of approximately 540 F.

The refined type metal was found to have'o'nly- 0.01% tellurium after scraping the melt for ten minutes during liquation of the metal.

In light of the above test results it will be evident I have devised a singularly simple and eflicient method for treating metals and alloys This is a decided improvement over the to remove impurities which does not require the addition of costly reagents. Furthermore, my newlprocess can be carried out with inexpensive 1 equipment and is more easily performed than the intricate processes used prior to my discovery.

While I have described my process in detail with respect to certain metals and alloys, it will be understood that the process is applicable broadly to metallurgical refining processesand that various changes may be made within the scope of the invention as defined by the appended claims.

What is claimed is: 1. The process of refining metals or alloys of the group consisting of lead and tin to remove impurities which are present in amounts not greatly in excess of the amount which is soluble in a melt formed of the impure metal being refined and will float to the surface of said melt' comprising the steps of liquating the metal at a substantially constant temperature wherein the impurit es tend to segregate from the melt and approach the surface thereof, simultaneously skimming the surface ofthe melt in a continuous manner without appreciably disturbing the body of the melt to scrape aside the skimmings and expose fresh metal for oxidation, and continuing the operation at said temperature until the impurities havebeen lowered to the desired point.

2. In the process of refining lead and tin metals or alloys to remove impurities which are present 1 in amounts not greatly in'excess of the amount,

which is soluble in a melt formed of the impure.

meta1.being refined and which insoluble impurities will float or migrate to thesuri'ace t: we

melt, the stepsoi' heating the metal an oxidissolubility of the impurities in the melt is at a minimum, skimming the surface of the melt-continuously while maintaining said temperature substantially constant for a predetermined length of time to remove substantially all of said-in soluble impurities, .said skimming operation be- Y metals or alloys .of the group consisting of lead and fti'n when present in small percentage amounts of the order of 0.01 or in amounts not greatly in excess of the amount which is soluble Y in a melt formed of the impure metal being reing performedwithout substantially agitating or stirring the body of the melt to efiect mechanical occlusion vof the impuritiesin the'skimmings as they segregate from the metal and rise to-the surface of the melt. i

3. The process of removing small amounts of Y impurities from type metals wherein said impurities are present in amounts not greatly in excess of the amounts which are soluble in a melt formed I of the impure metal and which: impurities will float to the surface of said melt comprising heating the metal while exposed to air to substantially its liquid state, holding the metal at this I temperature, simultaneously and continuously scraping at least a portion of the melt surface a to repeatedly expose fresh metal tooxidation without appreciably disturbing the body of the melt forming'skimmings which are continually brushed aside, continuing the operation to effect occlusion of the impurities in the skimmings until the content of said impurities in the melt has been lowered substantially to an amount below whichothe impurities are soluble in said melt.

4. The process of removing small amounts of sulphur from metals or alloys of the group consisting'of lead and tin wherein said sulphur is curs, maintaining said melt at this temperatureflned and will float to the surface of said melt.

comprising heating the metal. in a receptacle while exposed to oxidation by surrounding air toa' temperaturewherein liquation of the melt cc- 8. The process of removing while concurrently lightly skimming the surface of the melt to scrape aside the skimming; and repeatedly expose fresh metal to the air without disturbing the body of said melt andcontinuing' said treatment, to effect the mechanical occlusion of the impurities in the skimmings as said impurities migrate to the surface of the'melt whereby the same can be removed with said 'skimmings to reduce the content of impurities to the desired 7. The process 'of removing impurities from lead and tin metals or alloys thereof wherein said impurities are present in'amounts not greatly in excess of the amounts which are soluble in a melt formed of the metal and containing said impurities which impurities float or migrate to the surface of the melt comprising heating the metal to produce a melt, maintaining the melt in an oxidizing atmosphere to form oxide skimmings on the surface of the melt,'simultaneously present in an amount not greatly in excess of the amount which is soluble in a melt formed of the i impure'metal and floats to the surface of. said melt comprising heating the metal until it is substantiailly in a liquid state, holding the temperature at thi point while maintaining said liquid metal in-an oxidizing. atmosphere to form oxide skimmings on the surface of the melt, simultaneously scraping atleast a portion of the surface of the melt to scrape the skimmings aside without stirring the body of the melt, rcontinuing'the scraping operation while maintaining the melt at said temperature to mechanically collect the sulphur or compounds thereof in the skimmings,

and removing the same therewith. Y 5. The process of removing residual impurities from lead and tin base solder metal wherein said face of said melt which comprises heating the metal until it is substantially in a, liquid state,

holding the temperature at this point while main- 1 taiuing said liquid metal in an oxidizing atmos 1 phere to form oxide skimmings on the surface of the melt, simultaneously scraping at least a portion of the surface of the melt to scrape the skimmings aside continuing the scraping opera- I a melt formed of the metal and on Y tion while maintaining the body of the melt in x a quiescent state to mechanically collect the impurities or 'compoundsthereof inthe skimmings, and removing the same therewith.

skimming the surface of the melt in a continuous manner scraping aside the skimmings while the body of the melt remains in a quiescent state whereby the insoluble impurities which rise to the surface of the melt'are mechanically occluded in the skimmings and scraped aside therewithand continuing said treatment until the content of said impurities in the melt has been substantially lowered orreduced to a value below which amount the impurities aresoluble in the melt.

. 8. The process of removing impurities from lead and tin metals or alloys thereof wherein said impurities'are present in amounts not greatly in excess of the amounts which are soluble in containing said impurities which impurities will float or migrate to the surface of said melt comprising establishing a melt of the impure metal, maintaining the melt in an oxidizing atmosphere to form oxide skimmings on the surface of the melt, skimming the melt in a continuous manner without stirring the body of the melt whereby the insoluble impurities as they rise to the surface of the melt are mechanically occluded in the skimmings and subsequently. removed therewith and continuing the simultaneous oxidation and skimming oper- I ,ation to effect the mechanical occlusion of said impurities in the skimmings as they rise to the surface of the melt until the content of said impurities in the melt has been substantially lowimpurities are soluble in themelt.

cred or reduced to an amount belowwhich the Y 

